Electric low-voltage fuse having terminal bars

ABSTRACT

A polyphase fuse has a housing shaped substantially prismatically and subdivided into a plurality of chambers each provided for a phase fuse unit, or pole fuse unit, of the polyphase fuse. Each of the chambers contains a pair of terminal bars spaced by the housing itself so as to dispense with additional insulating spacers arranged between each pair of terminal bars. The juxtaposed surfaces of each pair of terminal bars are provided with fuse-link-receiving grooves. Each fuse link means includes a groove-engaging spacing tab and a substantially C-shaped center portion positioned generally transversely to the pair of terminal bars. The fuse link means of each phase unit of the polyphase fuse are superimposed and form a stack, the spacing between the contiguous C-shaped center portions thereof being determined by the length of their spacing tabs.

United States Patent Salzer [151 3,673,533 [451 June 27, 1972 [54]ELECTRIC LOW-VOLTAGE FUSE HAVING TERMINAL BARS [72] Inventor: ErwinSalzer, Waban, Mass.

[73] Assignee: The Chase-Shawmut Company, Newburyport, Mass.

22 Filed: Aug. 17, 1971 21 Appl.No.: 172,470

[52] US. Cl ..337/161, 337/231, 337/252, 337/295 [51] Int. Cl. ..I'IOlh85/08, HOlh 85/12, H0lh 85/20 [58] Field ofSearch ..337/158,l59,161,164, 227, 337/228, 229, 230, 231, 232, 234, 235, 236, 237,

[5 6] References Cited UNITED STATES PATENTS 5/1964 Jacobs, .lr...337/161 X 4/1937 Carney "337/237 X 1,604,477 10/1926 Ogle ..337/229Primary Examiner-Bemard A. Gilheany Assistant Examiner-Dewitt M. MorganABSTRACT A polyphase fuse has a housing shaped substantiallyprismatically and subdivided into a plurality of chambers each providedfor a phase fuse unit, or pole fuse unit, of the polyphase fuse. Each ofthe chambers contains a pair of terminal bars spaced by the housingitself so as to dispense with additional insulating spacers arrangedbetween each pair of terminal bars. The juxtaposed surfaces of each pairof terminal bars are provided with fuse-link-receiving grooves. Eachfuse link means includes a groove-engaging spacing tab and asubstantially C-shaped center portion positioned generally transverselyto the pair of terminal bars. The fuse link means of each phase unit ofthe polyphase fuse are superimposed and form a stack, the spacingbetween the contiguous C-shaped center portions thereof being determinedby the length of their spacing tabs.

5 Claims, 4 Drawing Figures PATENTEDJUNZ? 1972 ERWIN SALZER ELECTRICLOW-VOLTAGE FUSE HAVING TERMINAL BARS BACKGROUND OF THE INVENTION Thisinvention is related to the subject-matter disclosed in the copendingpatent applications of Frederick J. Kozacka, filed Dec. 8, 1970, Ser.No. 96,1 for COMPACT POLYPl-IASE FUSE; Kenneth W. Swain, filed Dec. 15,1970, Ser. No. 98,422; for POLYPHASE FUSE WITH BLOWN FUSE INDICATOR INEACH PHASE; and Richard A. Belcher et al., filed Aug. 24, 1971 Ser. No.174,455; for ELECTRIC LOW-VOLTAGE FUSE.

The aforementioned patent applications relate to polyphase fusestructures wherein the conventional insulating spacers between theterminal bars of each phase unit, or pole unit, are dispensed with. Thisis also one of the objects of the present invention. The above patentapplications further relate to polyphase fuse structures intended tominimize the spacing between the terminal bars thereof, and this islikewise an object of the present invention. The present inventionprovides means which make it readily possible to load stacks of fusibleelement means into a housing cavity intended to house a phase unit ofthe polyphase fuse, and to maintain the proper spacing between thefusible element means. Another object of the present invention is topack a dense array of fusible element means into a relatively narrowspace without impairing the dielectric recovery of the arc gaps formedincident to blowing of a phase unit of the polyphase fuse so as not toendanger the effectiveness thereof. Still another object of the presentinvention is to provide an array of fusible element means tending topreclude incident to blowing of the fuse the formation by magneticaction of undesirable and dangerous concentrations of products of arcingor plasma.

SUMMARY OF THE INVENTION Fuses embodying this invention include ahousing of an electric insulating material defining an elongated cavitysubstantially closed at one side of said housing and open at theopposite side thereof. A pulverulent arc-quenching filler is arrangedinside of said cavity and the latter is closed by a cover of electricinsulating material. A pair of terminal bars is arranged inside and atopposite sides of said cavity. The aforementioned pair of terminal barsis affixed to said housing and has ends projecting away from saidhousing. The pair of terminal bars is spaced from each other solely bysaid housing under exclusion of any additional spacing means arrangedbetween the juxtaposed surfaces of said pair of terminal bars. Said pairof terminal bars is provided with a relatively wide groove extending ina direction longitudinally of said pair of terminal bars. The pair ofterminal bars is conductively interconnected by a plurality of ribbonfuse link means of which each includes a pair of terminal tabs arrangedsubstantially parallel to and coplanar with said juxtaposed surfaces ofsaid pair of terminal bars and each having substantially the same widthas said groove and engaging said groove in one of said pair of terminalbars. Each of said plurality of fuse link means further includes acenter portion arranged between and angularly related to said pair ofspacing tabs and arranged generally transversely to said pair ofterminal bars, said plurality of fuse link means being superimposed in adirection longitudinallyof said pair of terminal bars and forming astack, and the constituent fuse link means of said stack being spacedfrom each other by said spacing tabs thereof.

BRIEF DESCRIPTION OF DRAWINGS FIG. 1 is a diagrammatic isometric view ofa polyphase fuse embodying this invention as seen from the rear end, orcover end, thereof;

FIG. 2 is a vertical section across the structure of FIG. 1 taken atright angles to the front surface and to the rear surface of thestructure of FIG. 1;

FIG. 3 is a section along 3-3 of FIG. 2; and

FIG. 4 is an elevation of the fuse link means of the structure of FIGS.1-3.

DESCRIPTION OF PREFERRED EMBODIMENT Reference character 1 has beenapplied to generally designate a substantially prismatic housing ofelectric insulating material subdivided by internal partitions la intothree separate chambers or compartments lb, each closed at all sidesthereof except one side, or except its rear side R. Casing l ispreferably a molding of an appropriate synthetic resin. The threechambers or cavities lb are filled with a pulverulent arc-quenchingfiller, preferably quartz sand. Reference numeral 2 has been applied inFIGS. 3 and 4 to indicate this body of pulverulent arc-quenching filler.Cover means 3 are provided for closing the open sides of chambers, orcavities, lb. Cover means 3 have partitions 3a arranged in registry withthe partitions In of housing 1. In other words, each of partitions laand each of partitions 3a are arranged in a common vertical plane. Thepartitions 3a in cover means 3 subdivide the latter into three separatechambers 3b of which each communicates with but one of chambers orcavities lb, and is separated from all other chambers or cavities lb.The body of pulverulent arcquenching filler 2 in 'each of chambers lbextends into one of the chambers 3b defined by cover means 3. As aresult of this geometry housing 1 and cover means 3 define jointly threeseparate composite chambers or cavities lb, 3b of which each is filledwith a separate body of pulverulent arc-quenching filler 2. Cover 3 isscrewed to housing 1 by four screwthreaded studs 4 shown in FIG. 1.

A pair of terminal bars 5 is arranged in each of chambers or cavitieslb. Each pair of terminal bars 5 is arranged at up posite surfaces ofchambers lb and extends from the open or rear side of chambers orcavities lb to the side thereof opposite to the open side, which side isthe front side of the polyphase fuse structure. The ends of terminalbars 5 adjacent cover means 3 are bent out of the plane of the remainingpart of bars 5 and are terminals for connecting the polyphase fuse intoa polyphase circuit. In FIG. 1 but the inside of one of the threechambers or cavities lb is fully shown, and but one pair of terminalbars 5 is fully shown. The internal arrangement of parts is the same inall three chambers lb and the terminal bars 5 in all three chambers aresupposed to have bent ends to be used as terminals, or connectors.Terminal bars 5 are held in position by means of screws 6 projectingthrough the top wall and through the bottom wall of housing 1. The outerends of screws 6, i.e. the heads thereof, may be covered with aninsulating material or sealing material to preclude physical contactwith any part, or parts, which have a potential above ground potential.These insulating seals have not been shown in the drawings.

A plurality of ribbon fuse link means 7 interconnects conductively eachpair of terminal bars 5. Fuse link means 7 are embedded in arc-quenchingfiller 2. The length of each fuse link means 7 exceeds the spacingbetween the pair of terminal bars 5 which are conductivelyinterconnected by it.

Each terminal bar 5 is provided with a relatively wide groove 5aextending in a direction longitudinally thereof. The grooves 5a of eachpair of bars 5 are arranged on the juxtaposed surfaces of the former andthe fuse link means 7 of FIG. 4 are inserted into pairs of juxtaposedgrooves 5a in bars 5 by means of spacer tabs 7a.

Cover 3 is provided with three apertures 30 for filling the threecomposite chambers or cavities lb,3b formed by housing 1 and by cover 3with pulverulent arc-quenching filler. Each aperture 3c is sealed by aplug 8 which may be formed by a cured synthetic resin, e.g. an epoxyresin.

The front side F of housing 1 is provided with three apertures 10 havinga relatively large diameter. The front wall of housing 1 forms integralhollow projections 1d each extending into one of chambers or cavitieslb. The aforementioned hollow projections Id are preferably in the shapeof solids of revolution, and each projection 1d has a relatively smallaperture 1: at the innermost end thereof, i.e. in the end thereofprojecting farthest into one of chambers or cavities lb. A spring-biasedblown fuse indicator is arranged in the space between apertures 10 and1c. The blown fuse indicator ineludes indicating button 9, helicalbiasing spring 9a, spring supporting cap 9b and tie rod 90. Tie rod 90has an axially outer end engaging indicating button 9 and an axiallyinner end which is flattened and arranged inside of hollow projection1d. Reference numeral 10 has been applied to indicate a high ohmicresistance restraining wire conductively interconnecting terminal bars5. Restraining wire 10 is substantially V- shaped, and the convergingend thereof extends through aperture 12 into hollow projection 1d and isthreaded through a hole provided in the axially inner flattened end oftie rod 90. The aperture Ie in hollow projection 1d is sealed by a bodyof sealing paste which retains its pastelike consistence. Siliconegrease is the preferred sealing paste since relatively high temperaturesmay occur at the location of aperture 1e.

Housing 1 forms an assembly jig or fixture for assembling the partsintended to be arranged therein. First the terminal bars 5 are insertedinto housing 1 and firmly held in position therein by screws 6, or otherappropriate fastener means. Thereupon fuse link means 7 are insertedwith the tabs 7a thereof into the grooves 5a of bars 5, and solder inpaste form is inserted into the grooves 5a. This makes the assemblyready for induction soldering. During this process the casing 1 remainsrelatively cool, and the generation of heat occurs primarily at thelocation where it is intended to form solder joints. Thereupon somesilicone grease is placed adjacent the apex of projection 1d on theinner surface thereof and parts 9,90,9b and 9c are arranged in theirrespective place and the ends of restraining wire 10 extending from tierod 90 are threaded through the aperture 12 in projection 1d. The endsof restraining wire 10 may be affixed to terminal bars 10 by means ofscrews ll. Then cover 3 is attached to housing 1 by means of screwthreaded studs 4 and quartz sand 2 is filled into the three compositechambers or cavities 1b,3b through the apertures 3c in cover 3. Finallyapertures 30 are filled by sealing means 8.

This way of assembling polyphase fuses is superior to the moreconventional way involving the insertion of pre-assembled fuse units,one for each phase, into a common housing for the polyphase fuse. Theaforementioned prior art method of insertion of pre-assembled fuse unitseach into a separate chamber of a common housing requires the additionof spacing means between the pair of spaced terminal bars of each phaseunit. Deletion of additional spacing means for the terminal barsdecreases significantly the cost of manufacture since it reduces boththe cost of material and of labor.

It will be apparent from the above that in the structure which has beendisclosed housing 1 forms the only spacing means for spacing pairs ofterminal bars 5, thus dispensing with the need of providing additionalspacing means for each pair of terminal bars 5.

Upon blowing of the fuse fulgurites take the place of ribbon fuse linkmeans 7, causing a voltage to appear across bars 5. As a result,restraining wire 10 fuses and pins 9 are propelled forwardly by springaction.

Each groove 5 is relatively wide. The spacing tabs 7a are arrangedsubstantially parallel to and coplanar with the juxtaposed surfaces ofterminal bars 5 and have substantially the same width as grooves 5a.Each fuse link means 7 engages juxtaposed grooves 5a with its spacingtabs 7a. The center portions of fuse link means 7 are arranged betweentheir spacing tabs 7a, angularly related to the latter and positionedgenerally transversely to terminal bars 5. The fuse link means 7 of eachphase unit of the polyphase fuse are superimposed in a directionlongitudinally of terminal bars 5 and form a stack. The constituent fuselink means 7 of this stack are spaced from each other by their spacingtabs 7a. Each fuse link means 7 establishes a pair of parallel currentpaths as clearly shown in FIG. 7. When the fuse structure is assembledthese current paths are separated by the arc-quenching filler 2. Allfuse link means 7 are connected in parallel.

The center portion of each fuse link means 7 is curved and concave atthe side thereof juxtaposed to the blown fuse indicator side of cavitylb formed by housing 1 and convex at the side thereof juxtaposed tocover means 3. The current paths established by bars 5, spacer tabs 7aand the center portions of fuse link means 7 preclude a dangerousconcentration of products of arcing at the end of cavity lb adjacent theblown fuse indicator. Such concentration of are products is a criticalfactor in the'design of polyphase fuses and must be avoided by allavailable means if the spacing between terminal bars 5 is intended to beminimized and the current-carrying capacity and interrupting capacity ofthe polyphase fuse is intended to be maximized. The aforementionedgeometry of the spacing tabs 7a and the center portions of fuse linkmeans 7 make it even possible to arrange two fusible elements or ribbonfuse links in narrowly spaced pairs, as clearly shown in FIGS. 3 and 4.Even if the fuse structure is provided with a dense array of fusibleelement means 7, as shown in the drawings, and even if the spacingbetween terminal bars 5 is but slightly more than 1 inch, considering avoltage rating of 600 volts, there is no tendency of merger of thefulgurites which take the place of the center portions of fuse linkmeans 7 upon blowing of the fuse. This can readily be explained by theconfiguration of the magnetic field resulting from the geometry of thefuse structure.

Another favorable factor resides in the fact that fuse link means 7curve away from the end of cavity lb where the blown fuse indicatormechanism is arranged. This maximizes the spacing between the fulguriteclosest to the blown fuse indicator mechanism and the latter which is animportant factor in regard to the capability of the fuse structure tooperate successfully even under the most adverse conditions. Testsconducted with fuse link means whose center portion had a configurationdifferent from the C-configuration shown in FIGS. 1 and 2 resulted inconsiderably denser and considerably narrower spaced fulgurites at theend of cavity lb adjacent the blown fuse indicator. These tests showedalso a strong tendency of dielectric breakdown at the aforementioned endof cavity 1b and a bumback of some fusible elements or fuse links intobars 5. Tests conducted with the structure of FIGS. 1 and 2 underidentical conditions as the aforementioned tests showed a bumback offuse link means 7 which stopped short of bars 5 and formation offulgurites of substantially the same or uniform character at all pointsof each chamber of the polyphase fuse structure wherein blowingoccurred.

The drawings show a polyphase fuse structure intended for a relativelyhigh current rating, e.g. 150 ms amps. Where the intended current ratingis smaller, some of the fusible element means 7 may be deleted. Thethinning out or reduction of density should be effected at the end ofcavity lb immediately adjacent the blown fuse indicator mechanism, or atthe end of cavity lb remote from the ends 50 of bars 5 projecting awayfrom housing 1.

The structure according to this invention lends itself to fast andinexpensive assembly by resorting to an appropriate assembly jig. Such ajig may include a pair of spaced grooved bars similar to the terminalbars 5 of the polyphase fuse structure, a spacer for spacing the bars ofthe jig, and a plunger for the ejection of the fuse link means from thejig. The jig is loaded with the desired number of fuse link means 7 byinserting the spacing tabs thereof into the grooves of the jig bars.Then the jig is positioned relative to housing 1 containing terminalbars 5 in such a way that the grooves 5b of terminal bars 5 are inalignment with the corresponding grooves in the bars of the jig.Thereupon the entire array of fusible element means previously placed inthe jig is transferred with one single stroke of the jigs ejectionplunger into grooves 5b of terminal bars 5. The aforementioned ribbonlink ejection plunger has a stroke limited by appropriate abutmentmeans. This abutment feature determines the position of the stack offusible element means inside of cavity 1b being transferredsimultaneously as a unit from the assembly jig into the polyphase fusestructure.

It will be apparent from FIG. 3 that the restraining wire 10 of theblown fuse indicator mechanism is arranged inside of a gap 7b formedbetween the pair of parallel ribbons, or parallel current paths, of eachfuse link means 7. In other words, gaps 7b define a plane in which planerestraining wire 10 is arranged. Thus the space between terminal bars 5accommodates only current carrying and current interrupting means, butno insulating means for positioning terminal bars 5 and spacing thelatter.

I claim as my invention:

1. An electric low-voltage fuse including a. a housing of an electricinsulating material defining an elongated cavity substantially closed atone side of said housing and open at the opposite side thereof;

b. a pulverulent arc-quenching filler inside said cavity; c. a cover ofan electric insulating material covering the open side of said cavity;

d. a pair of terminal bars arranged inside and at opposite sides of saidcavity and affixed to said housing and having ends projecting away fromsaid housing, said pair of terminal bars being spaced from each othersolely by said housing under exclusion of any additional spacing meansarranged between the juxtaposed surfaces of said pair of terminal bars,each of said juxtaposed surfaces of said pair of terminal bars beingprovided with a groove having a relatively large width and extending ina direction substantially longitudinally of said pair of terminal bars;and

e. a plurality of ribbon fuse link means conductively intersaidplurality of fuse link means being superimposed in a directionlongitudinally of said pair of terminal bars and forming a stack, andthe constituent fuse link means of said stack being spaced from eachother by said spacing tabs thereof.

2. An electric fuse as specified in claim 1 wherein said center portionof each of said plurality offuse link means is curved and concave at theside thereof juxtaposed to said closed side of said cavity and convex atthe side thereof juxtaposed to said cover.

3. An electric fuse as specified in claim 1 wherein said center portionof each of said plurality of fuse link means includes a plurality ofspaced current paths separated from each other by said pulverulentarc-quenching filler.

4. An electric fuse as specified in claim 1 wherein a. said housing hasa projection at said one side thereof entering into said cavity andaccommodating a blown fuse indicator mechanism; and wherein b. saidcenter portion of each of said plurality of fuse link means is curvedand concave at the side thereof juxtaposed to said projection and convexat the side thereof juxtaposed to said cover.

5. An electric fuse as specified in claim 4 wherein a. said centerportion of each of said plurality of fuse link means includes a pair ofspaced current paths forming a gap therebetween; and wherein b. saidblown fuse indicator mechanism includes a restraining wire normallyshunted by said plurality of fuse link means and arranged in a planedefined by said gap formed by said pair of current paths of said centerportion of each of said plurality of fuse link means.

l t I! I I

1. An electric low-voltage fuse including a. a housing of an electricinsulating material defining an elongated cavity substantially closed atone side of said housing and open at the opposite side thereof; b. apulverulent arc-quenching filler inside said cavity; c. a cover of anelectric insulating material covering the open side of said cavity; d. apair of terminal bars arranged inside and at opposite sides of saidcavity and affixed to said housing and having ends projecting away fromsaid housing, said pair of terminal bars being spaced from each othersolely by said housing under exclusion of any additional spacing meansarranged between the juxtaposed surfaces of said pair of terminal bars,each of said juxtaposed surfaces of said pair of terminal bars Beingprovided with a groove having a relatively large width and extending ina direction substantially longitudinally of said pair of terminal bars;and e. a plurality of ribbon fuse link means conductivelyinterconnecting said pair of terminal bars each including a pair ofspacing tabs arranged substantially parallel to and coplanar with saidjuxtaposed surfaces of said pair of terminal bars and havingsubstantially the same width as said groove and engaging said groove ineach of said pair of terminal bars, each of said plurality of fuse linkmeans further including a center portion arranged between and angularlyrelated to said pair of spacing tabs and positioned generallytransversely to said pair of terminal bars, said plurality of fuse linkmeans being superimposed in a direction longitudinally of said pair ofterminal bars and forming a stack, and the constituent fuse link meansof said stack being spaced from each other by said spacing tabs thereof.2. An electric fuse as specified in claim 1 wherein said center portionof each of said plurality of fuse link means is curved and concave atthe side thereof juxtaposed to said closed side of said cavity andconvex at the side thereof juxtaposed to said cover.
 3. An electric fuseas specified in claim 1 wherein said center portion of each of saidplurality of fuse link means includes a plurality of spaced currentpaths separated from each other by said pulverulent arc-quenchingfiller.
 4. An electric fuse as specified in claim 1 wherein a. saidhousing has a projection at said one side thereof entering into saidcavity and accommodating a blown fuse indicator mechanism; and whereinb. said center portion of each of said plurality of fuse link means iscurved and concave at the side thereof juxtaposed to said projection andconvex at the side thereof juxtaposed to said cover.
 5. An electric fuseas specified in claim 4 wherein a. said center portion of each of saidplurality of fuse link means includes a pair of spaced current pathsforming a gap therebetween; and wherein b. said blown fuse indicatormechanism includes a restraining wire normally shunted by said pluralityof fuse link means and arranged in a plane defined by said gap formed bysaid pair of current paths of said center portion of each of saidplurality of fuse link means.